After some digging I’ve located what I believe is the original stock art image of the tree used by both Cynthia Occelli and Ann Voskamp.
It was designed by an artist named Tolchik who is listed as an Illustrator / Vector Artist. Her portfolio with Shutterstock is found here.
The image is available for purchase, with an extended license, via Shutterstock, CanStock, 123RF and several other stock photo companies.
It is certainly possible that Mrs. Voskamp and Ms. Occelli coincidentially chose to use the same image.
Ann Voskamp and Plagiarism – Part II
Ann Voskamp and Plagiarism – Part III
Ann Voskamp and Plagiarism – Part IV